The present invention relates to methods, processes and apparatii for development of images, and more specifically, to electrode members for use in a developer unit in electrophotographic machines. Specifically, the present invention relates to methods and apparatii in which at least a portion of a development unit electrode member is coated with a coating material, and in embodiments, a low surface energy coating material comprising a partly fluorinated polymer. In embodiments, the partly fluorinated polymer is soluble in fluorinated solvents. In embodiments, electrode member history, damping and/or toner accumulation is controlled or reduced. In embodiments, the coating comprises a partly fluorinated polymer, a fluorinated solvent, and a metal material. In embodiments, the metal material is a superconductor or a superconductor precursor. In embodiments, the partly fluorinated polymer acts as a co-solubilizer, making soluble in fluorinated solvents, materials which are not normally soluble in fluorinated solvents.
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential so as to sensitize the photoconductive member thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. This records an electrostatic latent image on the photoconductive member. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Two component and single component developer materials are commonly used. A typical two component developer material comprises magnetic carrier granules having toner particles adhering triboelectrically thereto. A single component developer material typically comprises toner particles. Toner particles are attracted to the latent image forming a toner powder image on the photoconductive member. The toner powder image is subsequently transferred to a copy sheet. Finally, the toner powder image is heated to permanently fuse it to the copy sheet in image configuration.
One type of single component development system is a scavengeless development system that uses a donor roll for transporting charged toner to the development zone. At least one, and up to a plurality of electrode members are closely spaced to the donor roll in the development zone. An AC voltage is applied to the electrode members forming a toner cloud in the development zone. The electrostatic fields generated by the latent image attract toner from the toner cloud to develop the latent image.
Another type of a two component development system is a hybrid scavengeless development system, which employs a magnetic brush developer roller for transporting carrier having toner adhering triboelectrically thereto. A donor roll is used in this configuration also to transport charged toner to the development zone. The donor roll and magnetic roller are electrically biased relative to one another. Toner is attracted to the donor roll from the magnetic roll. The electrically biased electrode members detach the toner from the donor roll forming a toner powder cloud in the development zone, and the latent image attracts the toner particles thereto. In this way, the latent image recorded on the photoconductive member is developed with toner particles.
Various types of development systems have hereinbefore been used as illustrated by the following disclosures, which may be relevant to certain aspects of the present invention.
U.S. Pat. No. 4,868,600 to Hays et al., the subject matter of which is hereby incorporated by reference in its entirety, describes an apparatus wherein a donor roll transports toner to a region opposed from a surface on which a latent image is recorded. A pair of electrode members is positioned in the space between the latent image surface and the donor roll and is electrically biased to detach toner from the donor roll to form a toner cloud. Detached toner from the cloud develops the latent image.
U.S. Pat. No. 4,984,019, to Folkins, the subject matter of which is hereby incorporated by reference in its entirety, discloses a developer unit having a donor roll with electrode members disposed adjacent thereto in a development zone. A magnetic roller transports developer material to the donor roll. Toner particles are attracted from the magnetic roller to the donor roller. When the developer unit is inactivated, the electrode members are vibrated to remove contaminants therefrom.
U.S. Pat. No. 5,124,749 to Bares, the subject matter of which is hereby incorporated by reference in its entirety, discloses an apparatus in which a donor roll advances toner to an electrostatic latent image recorded on a photoconductive member wherein a plurality of electrode wires are positioned in the space between the donor roll and the photoconductive member. The wires are electrically biased to detach the toner from the donor roll so as to form a toner cloud in the space between the electrode wires and the photoconductive member. The powder cloud develops the latent image. A damping material is coated on a portion of the electrode wires at the position of attachment to the electrode supporting members for the purpose of damping vibration of the electrode wires.
U.S. Pat. Nos. 5,300,339 and 5,448,342 both to Hays et al., the subject matter each of which is hereby incorporated by reference in their entirety, disclose a coated toner transport roll containing a core with a coating thereover.
U.S. Pat. No. 5,172,170 to Hays et al., the subject matter of which is hereby incorporated by reference in its entirety, discloses an apparatus in which a donor roll advances toner to an electrostatic latent image recorded on a photoconductive member. The donor roll includes a dielectric layer disposed about the circumferential surface of the roll between adjacent grooves.
Primarily because the adhesion force of the toner particles is greater than the stripping force generated by the electric field of the electrode members in the development zone, a problem results in that toner tends to build up on the electrode members. Accumulation of toner particles on the wire member causes non-uniform development of the latent image, resulting in print defects. The problem is aggravated by toner fines and any toner components, such as high molecular weight, crosslinked and/or branched components, and the voltage breakdown between the wire member and the donor roll.
One specific example of toner contamination results upon development of a document having solid areas, which require a large concentration of toner to be deposited at a particular position on the latent image. The areas of the electrode member corresponding to the high throughput or high toner concentration areas tend to include higher or lower accumulation of toner because of this differing exposure to toner throughput. When the printer subsequently attempts to develop another, different image, the toner accumulation on the electrode member will lead to differential development of the newly developed image corresponding to the areas of greater or lesser toner accumulation on the electrode members. The result is a darkened or lightened band in the position corresponding to the solid area of the previous image. This is particularly evident in areas of intermediate density, since these are the areas most sensitive to differences in development. These particular image defects caused by toner accumulation on the electrode wires at the development zone are referred to as wire history. FIG. 5 contains an illustration of wire contamination and wire history. Wire contamination results when fused toner forms between the electrode member and donor member due to toner fines and any toner components, such as high molecular weight, crosslinked and/or branched components, and the voltage breakdown between the wire member and the donor roll. Wire history is a change in developability due to toner or toner components sticking to the top of the electrode member.
Accordingly, there is a specific need for electrode members in the development zone of a development unit of an electrophotographic printing machine, which provide for a decreased tendency for toner accumulation in order to decrease wire history and wire contamination, especially at high throughput areas, and decreasing the production of unwanted surface static charges from which contaminants may not release. One possible solution is to change the electrical properties of the wire. However, attempts at decreasing toner build-up on the development wire by changing the electrical properties thereof, may result in an interference with the function of the wire and its ability to produce the formation of the toner powder cloud.
Other attempts at reducing the accumulation of toner and to retaining electrical properties resulted in developer coating formulations for portions of the electrode wires.
U.S. Pat. No. 5,761,587, the subject matter of which is incorporated by reference herein in its entirety, discloses low surface energy coatings over a portion of the electrode wire.
U.S. Pat. No. 5,787,329, the subject matter of which is incorporated by reference herein in its entirety, discloses organic coatings of development electrodes.
U.S. Pat. No. 5,805,964, the subject matter of which is incorporated by reference herein in its entirety, discloses inorganic coatings of development electrodes.
U.S. Pat. No. 5,778,290, the subject matter of which is incorporated by reference herein in its entirety, discloses composite coated development electrodes.
U.S. Pat. No. 5,848,327, the subject matter of which is incorporated by reference herein in its entirety, discloses coating compositions for development electrodes.
U.S. Pat. No. 5,999,781, the subject matter of which is incorporated by reference herein in its entirety, discloses additional coating compositions for development electrodes.
Although the above newer coating formulations provided the desired properties of low surface energy, electrical conductivity and favorable tribo-charging against most toners and/or developer compositions, these formulations introduced roughness onto the surface morphology of the wire coating, due to limitations of process grinding of mineral fillers into the coating systems. Even a slight roughness introduces sufficient surface area to contribute to increased contamination of toner and toner additives.
Therefore, it is still desired to provide a coating for electrode members which has a greater decreased tendency to accumulate toner and which also retains the electrical properties of the electrode member in order to prevent interference with the functioning thereof. There is an additional need for electrode members which have superior mechanical properties such as a hard surface to provide increased durability against severe wear the electrode member receives when it is repeatedly brought into contact with tough rotating donor roll surfaces. Another desired mechanical property is a smooth electrode coating surface in order to decrease contamination of toner and toner additives.